From 1994-1997 we ran a four year project to survey the terminus response of all the glaciers on Glacier Peak, Washington to climate change. This was a century after a climb in the region by C.E. Rusk. Chocolate Glacier is the largest of the east side valley glaciers. The average retreat of Glacier Peak glaciers from the LIA to the 1958 positions was 1640 m. Richard Hubley noted that North Cascade glaciers began to advance in the early 1950s, after 30 years of rapid retreat. The advance was in response to a sharp rise in winter precipitation and a decline in summer temperature beginning in 1944 (Hubley, 1956; Pelto and Hedlund, 2001). All ten glaciers on Glacier Peak advanced. Advances of Glacier Peak glaciers ranged from 15 to 480 m and culminated in 1978 (Pelto and Hedlund, 2001). All Glacier Peak glaciers that advanced during the 1950-1979 period emplaced identifiable maximum advance terminal moraines, that were fresh and easy to recognize in the 1990’s. By 1984, all the Glacier Peak glaciers were again retreating, the North Cascade Glacier Climate Project has monitored this retreat since 1984.
2005 Glacier Peak east side
Cliff Hedlund beneath Vista Glacier during 1994 expedition.
Beginning at 3050 m Chocolate Glacier descends to 1800 m today. When Rusk (1924) first saw this glacier he noted that it presented a dramatic sediment covered front. Immediately above the terminus it was heavily crevassed and quite active, indicating a slow retreat. This glacier which he named Cool Glacier had retreated little from the alpine meadows fringing the south side of the glacier. The terminus had already retreated 400 m up the narrow valley by 1906 from its LIA. A retreat of 1380 m occurred between 1906 and 1946. The retreat was noted to be particularly rapid during the 1920-1940 period by Austin Post. Glacier advance had begun by 1950. An advance from 1946-1955 of more than 200 m occurred (Hubley, 1956). The advance continued up until 1975 totaling 450 m. This was the largest advance of the Glacier Peak glaciers, probably due to the nature of the steep, narrow valley down which the glacier flows from 1960 m to the terminus. The glacier was approximately at this maximum position when mapped in 1984. In the next sequence of images the red line is the mapped 1984 terminus, green is 1998 and blue is 2009. During our visit in 1994 the glacier had retreated 210 m from the moraine it had generated. By 1998 the glacier had retreated 275 m, and was at the based of a steeper slope. By 2009 the glacier had retreated 500 m since 1984, ending at 1925 m, this is still the lowest of the east side glaciers.
1984 map view
1998 Google earth view
2009 Google Earth
Chocolate Glacier remains crevassed and active, but the degree of crevassing has decline from 1998 to 2009 as evidenced by this closeup of the 2000-2200 m region. It is hard to get a good view of this glacier from up close the best vantage is from across the Suiattle River valley, as seen below.
1998 Google Earth view
2009 Google earth view
2006 Glacier Peak from the east
2007 Glacier Peak from the east
In the 1990’s the North Cascade Glacier Climate Project undertook a study of all the glaciers around Glacier Peak, one century after they had been first observed by C.E. Rusk. This post focuses on one of those glaciers, Dusty Glacier on the Northeast side of the peak.
In 1940 J.B. Richardson of the Forest Service photographed many North Cascade glaciers surrounding Glacier Peak. From 1946-1958 William Long, of the Forest Service surveyed many glaciers throughout the North Cascades (Long, 1955). From 1950-1955 Richard Hubley, University of Washington, completed the first aerial glacier surveys of North Cascade termini, noting the beginning of an advance on many (Hubley, 1956). The USGS in 1960 began an annual aerial photographic survey of North Cascade glaciers that continued up through 1979. In 1984 the North Cascade Glacier Climate Project began annual terminus observations on 47 glaciers and mass balance measurements on ten of these (Pelto, 1996). The average retreat of Glacier Peak glaciers from the LIA to the 1958 positions was 1640 m. Richard Hubley noted that on Glacier Peak glaciers began to advance in the early 1950s, after 30 years of rapid retreat. The advance was in response to a sharp rise in winter precipitation and a decline in summer temperature beginning in 1944 (Hubley, 1956; Long, 1955 and 1956). Ten of the fifteen glaciers around Glacier Peak advanced, including all of the glaciers directly on the mountains slopes. Advances of Glacier Peak glaciers ranged from 15 to 480 m and culminated in 1978. All 11 Glacier Peak glaciers that advanced during the 1950-1979 period emplaced identifiable maximum advance terminal moraines. By 1984, all the Glacier Peak glaciers were again retreating. This retreat has been monitored by NCGCP. Two of the glaciers including Milk Lake Glacier and North Branch Whitechuck Glacier have disappeared.
The depth of snowpack even in Mid-August near the top of the Dusty Glacier is what drives the rapid movement and crevassing of the glacier. In the first image below the red arrow indicates the annual layer, which was 5.7 m thick in 1997. Thew second image has me standing at the terminus in 1994, which was still active even though it was retreating.
Dusty Glacier has the widest most fearsome crevasses of any glacier in the North Cascades. The glacier descends from 2750 m to 2560 m before plunging over an icefall. The glacier levels out in a basin at 2325 m, before descending a second icefall to its current terminus at 1960 m. Dusty Glacier joined with the North Guardian Glacier during the LIA, separating during the 1930’s. During the LIA the glacier advanced to 1465 m. The retreat of this glacier by 1906 when Rusk observed it had been only 400 m. The glacier ended in a basin that was filled with ice, though much of the ice was stagnant. This basin became known as Recession Basin, for the ensuing rapid retreat up until 1946 when the glacier had retreated out of the basin and ended just north of Recession Rock (R) at 2020 m. By 1955 advance was underway, an advance of 130 m had already occurred (Hubley, 1956). The advance ceased until 1967 when it began again, the glacier reaching another 150 m down into the upper part of Recession Basin at 1865 m. The terminus today is very active with extensive crevassing. In fact it is a true icefall. The glacier retreated 220 meters from its 1970’s advance moraine by 1994 during our first visit, 260 m by 1997-1998 at the time of our second visit and 400 meters by 2006 in the Google Earth imagery. The glacier remains quite crevassed though not nearly as much as in 1955. Below the first image is from 1955 taken by Richard Hubley, the second is in 2004, third in 2006 and last in 2008. In each image Recession Rock is labelled with a purple R, the maximum advance of the 1955-1970’s indicated by a orange arrow and the crevassed top of the lower icefall by a green arrow.
Google Earth images from 1998 and 2006 illustrate the retreat over the last 35 years. This glacier has not lost as much area as others around Glacier Peak, such as Milk Lake Glacier which disappeared, Honeycomb Glacier or Vista Glacier. The area loss has been more modest like on Suiattle and Kennedy Glacier.
At the turn of the century C.E. Rusk explored the glaciers around Glacier Peak that were retreating from their Little Ice Age maximum in the mid-19th century. The average retreat of Glacier Peak glaciers from the LIA to the 1958 map positions was 1640 m. From 1950-1955 Richard Hubley, University of Washington, completed the first aerial glacier surveys of North Cascade termini, noting the beginning of an advance on Glacier Peak that continued up through 1979. All ten glaciers on the slopes of Glacier Peak advanced ranged from 75 to 500 m and culminated in 1978. All 11 Glacier Peak glaciers that advanced during the 1950-1979 period emplaced identifiable maximum advance terminal moraines. A picture of the glacier from R.Luce during this advance shows a glacier with a strongly convex profile. During the 1993-1997 period the North Cascade Glacier Climate Project (NCGCP) surveyed the glaciers around the peak each summer, one century after C.E. Rusk did (Pelto and Hedlund, 2001). By 1984, all the Glacier Peak glaciers were again retreating. This peak even in summer provided some tough weather, including a 1995 August snow storm. Two other glaciers that were a focus of this study around Glacier Peak were Milk Lake, Vista and Honeycomb Glacier.
This post focuses on Kennedy Glacier which is the main glacier draining the west side of the Peak, left glacier in image below. Kennedy and Scimitar Glacier were joined during the LIA descending the Kennedy Creek valley to an elevation of 1315 m. Retreat from the LIA maximum of 1000 m had occurred by the turn of the century. By 1946 the glacier had retreated an additional 700 m to an elevation of 1960 m. In 1952 the glacier was advancing rapidly, as indicated by the 1955 photograph from Richard Hubley of the glacier from 1955. This advance continued up until 1975, the terminus having extended downslope 320 m to terminate at an altitude of 1785 m. By 1984 the terminus had begun to retreat. In 1994 the terminus had retreated 95 m and by 1997 151 m. A view of the terminus in 1993 indicates an active, crevassed terminus tongue, top image. In 1994 (miidle) and 1997 (below) the terminus is a well established vegetation and sediment line marking the 1970’s advance, burgundy arrows. The glacier has continued to retreat, in the 2006 and 2009 Google Earth imagery the orange line is the 1978 terminus, green line 1994, blue line 2006 and red line 2009. The left hand glacier is Kennedy the right hand Scimitar.. The glacier is continuing too retreat, but each summer retains significant accumulation, as evident in the crevasse measurements of snow depths on the upper Kennedy Glacier at 2800 meters. This indicates a glacier that can retreat to a new point of equilibrium with current climate.